Reversible displacement cell



Dec 119,, 1950 W. J. LEAS ET AL REVERSIBLE DISPLACEMENT CELL Filed June 14, 1947 Patented Dec 19, 1950 REVERSIBLE DISPLACEMENT oELL William J. Leas and Walter Dean Rose, Tulsa,

Okla., assignors to Standard Oil Development Gompany, a corporation of Delaware Application June 14, 1947, Serial No. 754,750

2 Claims.

The present invention is directed to an apparatus for the study 01' static equilibrium fluid phase distribution conditions attained in porous rock when (i) a fluid phase saturating the porous rock interstices is displaced therefrom by a second invading immiscible fluid phase, and (2) the displacement is reversed so that the second phase is displaced from the interstices by the immiscible fluid phase originally saturating the rock. This reversible displacement procedure somewhat simulates the history of oil migration into a water= or gas-filled subsurface formation and the production of oil from said formation under water or gas drive.

The principal object of the present invention is the provision of a reversible displacement cell useful in studies of the aforesaid character which is so constructed as to permit its use under the high pressures and temperatures prevailing in a subterranean reservoir from which a rock sample to be studied has been taken.

An additional object of the present invention is the provision of a cell of the character described in which wail effect on the displacement of one fluid by another immiscible fluid is eliminated. By wall effect is meant the sealing off of large areas of the surfacof the rock-sample by contiguous walls in contact therewith, thereby minimizing the eflective surface of the rock samples through which the invading fluid can enter.

A more specific object of the present invention is the provision of a cell of the character indicated in which means are provided for holding a sample of rock to be studied between two discs, one of which is preferentially oll-wetted and the other of which is preferentially water-wetted in such a manner that the entire surface of the rock sample between the discs is exposed to a displacing fluid and means are provided for introducing a displacing fluid into said cell without necessitating its travel through one of said discs.

Further objects and advantages of the present invention will appear from the following de-= tailed description of the accompanying drawing in which the single figure is a perspective view, partly in section, of one embodiment of the pres= ent invention.

Referring to the drawing in detail, numerals i and 2 represent metal plates spaced from each other by posts 3. Clamped between the metal plates is a metal cylinder 4, each end of which is separated from its adjacent metal plate by an permeable sealing disk 5 which may be conveniently made of rubber. Resting on each of the sealing disks is a metal disk 6 against which is held a semi-permeable disk l and 7'. One of these disks is preferentially permeable to oil and the other is preferentially permeable to water. In the embodiment shown the lower disk is the water permeable disk'l'. These disks may be made of porous ceramic material. Such a disk may be made preferentially water permeable by impregnating it with water and preferentially oil permeable by impregnating it with oil. The treatment of such a disk with a silicone, such as a chlorinated alkyl silicone, or with a metallic soap, such as lead oleate, increases its selective permeability for oil with respect to water.

These disks maybe composed of other materials to suit the purpose at hand; for example, cellophane sheets may be employed where high pressure operations are contemplated. It should be pointed out that the purpose of the disk is to permit the passage of one fluid phase while preventing the passage of another fluid phase immiscible with the first. When the disk is saturated with one fluid phase it will not be permeable to an immiscible fluid phase up to a certain pressure, depending on the pore size of the member. The smaller this pore size the higher will be the pressure. Therefore, for low pressure work ceramic materials are suitable and, in fact, are preferred because the use of membranes with smaller pores simply increases the time of operation. For high pressure operations, however, the membrane selected should be sumciently flne-pored to prevent the passage of the immiscible displacing fluid.

The rock sample to be studied is usually preformed into a cylinder 8 which is firmly clamped between the disks l and i. This sample has a diameter such as to leave an annular space Q between its curved surface and the inner wall of the cylinder 41. Tubes it pass through the wall of the cylinder (l to establish fluid connection between said annular space and outside fluid reservoirs.

At the upper end of the cell is an inlet tube M which passes through the upper plate, the rubber disk and the upper metal disk into the semi-permeable membrane. At the lower end of the cell is a similar tube H? which establishes fluid communication between the lower membrane and the outside of the cell.

In utilizing this apparatus for a study of displacement of water by oil and vice versa, the rock sample is saturated with the fluid to be displacedas, for example, salt water. The upper tube II is connected with a supply of oil and is also connected with a suitable pressure indicating means. The lower tube 12 is connected with a supply of saltwater and is also connected with a suitable pressure indicating means. The tubes are connected to the oil supply when displacing water by oil and to the water supply when displacing oil by water.

With the core, saturated with salt water, in place, the cell is immersed in an oil bath maintained at a temperature corresponding to the temperature of the reservoir from which the rock sample was obtained. The flow 01' oil to the cell is started through tubes In and tube H until there is built up in the cell a sufllclent pressure to establish across the membrane 1 a pressure diflerential corresponding to the capillary pressure condition which existed in the reservoir at the point from which, the sample was taken. Then the operator observes and measures the rate of displacement oi salt water from the'cell through tube l2. When no further water is displaced the operator can use the total quantity or water displaced to calculate the connate water or residual water left in the core sample which corresponds to that water retained in the rock in the reservoir after oil by intrusion had established the fluid equilibrium in the reservoir. The operation may then be reversed by flushing oil out of the annular space 8 with water, connecting tube II with a suitable volume measuring apparatus and connecting tubes l0 and I2 with the water supply. Then water pressure is built up in the cell to a point sumcient to establish a pressure in the cell corresponding to the water drive pressure available in the reservoir. With this pressure maintained, the rate and amount of oil displacement from the cell through tube II is measured. When no further oil is recovered the amount recovered is proportional to the ultimate recovery which may be expected from the reservoir.

It may be mentioned here that this cell is also adapted for studies of productivity of a reservoir under gas drive. In this case the oil permeable disk is arranged at the bottom oi the cell, which may be readily accomplished by inverting the position of the cell shown in the drawing. The gas then is introduced into the cell until the pressure inside the cell corresponding to the gas pressure in the reservoir is established. From this point on the procedure is the same as outlined above.

The nature and objects of the present invention having thus been set forth and a specific embodiment of the same given, what is claimed and desired to be secured by Letters Patent is:

l. A reversible fluid displacement cell for a rock sample comprising a pair of metal plates, means for drawing said plates toward each other in clamping position, a metal cylinder adapted to be clamped between said plates, impermeable sealing means disposed between each end of the cylinder and its adjacent plate, semi-permeable membranes arranged at'either end of the inside of said cylinder in a position to hold between them said rock sample, fluid conduit means communicating directly with the interior of said cylinder in a region between said membranes, and fluid conduit means communicating with the interior of said cell on the exterior side 01' each of said membranes.

2. A cell according to claim 1 in which the semi-permeable membrane on one end is selectively permeable to oil and'the semi-permeable membrane on the other end is selectively permeable to water.

WILLIAM J. LEAS. WALTER DEAN ROSE.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS 

